The invention disclosed and claimed herein generally pertains to the field of active optical detection systems, that is, to systems which project light into an environment and then detect projected light which has been reflected back from an object in the environment, the presence of the object in the environment being thereby indicated. More particularly, the invention pertains to systems of the above type wherein a single optical component is employed to both transmit light into the environment and receive light back from the environment, while maintaining transmitted and received light in isolation from one another. Even more particularly, the invention pertains to apparatus of the above type wherein only a single polarizer device is required to maintain isolation between transmitted or projected light and received light, i.e., to prevent cross-coupling therebetween, while detecting the presence of an object in an environment or providing other information related to the object.
In the past, active optical systems for detecting objects or bodies in an environment, such as an atmospheric environment, have generally required two different subsystems, a transmission system to project light into the environment, and a reception system to receive projected light which has been reflected back from an object. Separate transmission and reception systems have been necessary to avoid the phenomenon of cross-coupling, which occurrs when projected light travels from the light projector to the receiver, without first being reflected from an object in the environment. The ambient or background level of light detected by the receiver may thereby be made very high, so that receiver sensitivity is substantially diminished. Cross-coupling may occur as the result of backscatter, that is, the reflection of projected light back toward the receiver from fog or rain droplets.
In their invention, the applicants disclose apparatus which is capable of employing a single optical system to both project light into an environment and receive light back from the environment which has been reflected from an object or body therein, which is the subject of detection. At the same time, projected light from the receiver which has not been reflected from the object is prevented from reaching the light detection element of the system. Applicants thereby enable a significant reduction to be made in the cost, complexity, and number of components required for an active optical detection system. In Applicants' system, for example, only a single window or port is required to both project light into, and receive light from an environment which is being monitored for the presence of objects or bodies. Also, only a single light detection element is required to provide a signal which indicates the presence of an object in the environment in response to received light. In addition, in a system structured according to Applicants' invention, it is unnecessary to spatially separate the light projecting and receiving components thereof to avoid cross-coupling.